Plots of critical entry speed versus viscosity ratio for rough plates. Experimental results and theoretical predictions for smooth surface are presented as baselines ( λ s = 10 − 5 ). λ s = 5 × 10 − 5 is applied in theoretical prediction (Eq. (1)) for rough plates. Although the latter is very empirical, a higher value leads to worse agreement with experimental result. (a) Liquids: ethanol–glycerol solutions. (b) Liquids: water–glycerol solutions. θ e = 150 ° and θ e = 160 ° in panels (a) and (b), respectively, indicate that θ e > θ Y + 90 ° is more reasonable for the predictions.